The present invention is directed to an apparatus and method for the treatment of waste, particularly for the treatment of biologically treatable waste, such as septage.
As the focus on the environment increases, so does the need for improvements in the treatment of septage and other waste. Untreated septage—the liquid and solid material pumped from septic tanks, cesspools or other sewage waste sources—may contain any number of substances toxic to humans and the environment, including solvents, noxious organic and inorganic compounds and pathogens. Proper treatment of septage to reduce the noxious compounds and pathogens, in compliance with increased regulatory requirements, must be provided in an efficient, environmentally safe, yet economical process.
Septage is commonly disposed of by a process known as land application. This process typically involves pre-treating the septage by screening out solids, stabilizing the remaining waste, or “effluent,” chemically or biologically, and then applying the treated effluent to the ground by spraying, injecting or burying it. Land application is simple, cost-effective and uses relatively low energy. It also fertilizes and conditions the soil, decreasing the reliance on chemical fertilizers. Unfortunately, land application of septage suffers from a significant drawback, namely, land availability. Applying septage to land at levels that are not harmful to humans, animals or the environment require spreading it over a large area, which in many cases is unavailable or cost prohibitive.
Independent septage treatment plants have been implemented with some success. The general focus of these plants is to separate out solids (known as “biosolids”), which can be treated and used, for example, as fertilizer or energy sources, and neutralizing the remaining effluent before discharging it for land application or further treatment. These plants use such process as chlorine oxidation, aerobic and/or anaerobic biological treatment and other chemical treatment. Biological treatment including aerobic or anaerobic bacteria can be effective at reducing the amounts of harmful ammonia and nitrates in the septage. Physical means such as presses are also often used to dewater the septage. Some septage treatment plants also use alkali such as lime to condition and stabilize the septage before it is dewatered. The lime raises the pH of the septage, which reduces the attraction of vectors (rodents, birds, insects and other organisms that can transport pathogens) and helps to separate the solids from the liquids.
One such septage treatment plant is described in U.S. Pat. No. 7,070,693 to Kelly. Kelly discloses a septage processing facility that provides septage treatment in a series of steps. The steps include (1) screening and grinding the raw septage, (2) transferring the remaining effluent into large 13,000 gallon tanks; (3) pasteurizing the effluent in large batches of 10,150 gallons using a 300 horsepower boiler; (4) cooling the pasteurized effluent into cooling tanks where a floatable re-entrainment device removes floatable materials remaining in the effluent; (5) adding lime to the effluent sufficient to raise the pH to at least 12 for two hours and at least 11.5 for an additional 22 hours (per federal regulations); (6) pressing the lime septage mixture in a filter press to further dewater the mixture; (7) biologically treating the effluent in aerobic and anaerobic tanks; (8) clarifying the waste stream by running it through a sand filter system; and (9) treating the sand filtered waste stream by a UV disinfection system. Unfortunately, the Kelly process suffers from a number of inefficiencies. First, a large amount of energy is necessary to heat 10,125 gallons of liquid septage to 158 degrees, as required in the Kelly pasteurization step. Second, because the Kelly process pasteurizes such a large amount of material, it must then transfer that amount of material to cooling tanks and then on to the filter presses, requiring additional energy and increased area. In addition, the anaerobic treatment process requires the addition of large amounts of carbon dioxide, and also produces methane gas, which would make it difficult to safely house the system in an enclosed structure.